Radio station and method of processing user data with radio station

ABSTRACT

A radio station ( 1 ) includes a first part ( 1 A) and a second part ( 1 B). The second part ( 1 B) can be arranged so as to be physically separated from the first part ( 1 A) and is connected to the first part ( 1 A) via a transmission line ( 40 ) so as to be able to communicate with the first part. Each of the first part ( 1 A) and the second part ( 1 B) includes a digital signal processing unit ( 11 A,  11 B) and is capable of alternatively performing digital signal processing for user data. An analog signal processing unit ( 13 ) arranged in the second part performs analog signal processing including at least one of frequency conversion and power amplification to provide an air interface to a mobile station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of InternationalApplication No. PCT/JP2012/006366 entitled “Wireless Station and Methodof Processing User Data with Wireless Station,” filed on Oct. 3, 2012,which claims the benefit of the priority of Japanese Patent ApplicationNo. 2011-257477, filed on Nov. 25, 2011, the disclosures of each ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a configuration of a radio station(e.g., a radio base station, a relay station) used in a radiocommunication network.

BACKGROUND ART

A structure of a radio base station including a radio equipmentcontroller (REC) and a radio equipment (RE), which are separated fromeach other, is disclosed in Patent Literature 1 and Non-PatentLiterature 1. The REC and the RE are at least functionally separatedfrom each other. The REC and the RE are connected to each other throughan internal interface (communication interface) of the radio basestation. The REC and the RE may be arranged so as to be physicallyspaced apart from each other. In a typical layout, the REC is arrangedin a main building of a telecom carrier and the RE is arranged at aremote location near an antenna.

The REC is connected to an upper network (e.g., a core network of atelecom carrier). The REC plays a role in controlling and monitoring theentire radio base station and performing digital baseband signalprocessing. In this case, the digital baseband signal processingincludes layer-2 signal processing and layer-1 (physical layer) signalprocessing. The layer-2 signal processing includes at least one of (i)data compression/de-compression, (ii) data encryption, (iii)addition/removal of a layer-2 header, (iv) datasegmentation/concatenation, and (v) composition/decomposition of atransfer format by data multiplexing/de-multiplexing. In the case ofE-UTRA, as a specific example, the layer-2 signal processing includesprocessing of Radio Link Control (RLC) and Media Access Control (MAC).The physical layer signal processing includes channel coding/decoding,modulation/demodulation, spreading/de-spreading, resource mapping, andgeneration of OFDM symbol data (baseband OFDM signal) by Inverse FastFourier Transform (IFFT).

The RE plays a role in performing analog radio frequency (RF) signalprocessing, and provides an air interface to a mobile station. Theanalog radio frequency (RF) signal processing includes D/A conversion,A/D conversion, frequency up-conversion, frequency down-conversion, andamplification. The RE is also referred to as a remote radio head (RRH).

For example, in the case of a radio access network of a universal mobiletelecommunications system (UMTS), the REC provides a connection to aradio network controller (RNC) using an Iub interface for sending andreceiving user data (user plane data) and control data (control planedata). On the other hand, the RE provides a mobile station with an airinterface called a Uu interface.

In the case of Evolved Universal Terrestrial Radio Access (E-UTRA), theREC provides a connection to an evolved packet core (EPC) using an S1interface for sending and receiving user data and control data. On theother hand, the RE provides a mobile station with an air interfacecalled an LTE-Uu interface.

As described above, the separated structure of the radio base stationdisclosed in Patent Literature 1 and Non-Patent Literature 1 ischaracterized in that a part that performs analog RF signal processingis separated as the RE. This separated structure makes it possible toflexibly and effectively deal with an increase and a change in thefunctions implemented in the radio base station. In addition, thisseparated structure makes it possible to easily deal with independentadvancement of an analog RF technique and a digital baseband techniqueby separating the two techniques.

CITATION LIST Patent Literature

-   Patent literature 1: International Patent Publication No. WO    2004/095861

Non-Patent Literature

-   Non-Patent literature 1: Common Public Radio Interface (CPRI)    Specification V4.2 (2010-09-29), [online], September, 2010, Ericsson    A B, Huawei Technologies Co. Ltd, NEC Corporation, Alcatel Lucent    and Nokia Siemens Networks GmbH & Co. KG, [retrieved on Oct. 20,    2011], Internet <URL:http://www.cpri.info/spec.html>

SUMMARY OF INVENTION Technical Problem

It is predicted that as the traffic (user data) to be processed by theradio base station increases, the traffic between the REC and the REalso increases. However, in the separated structure disclosed in PatentLiterature 1 and Non-Patent Literature 1, the REC performs digitalsignal processing (channel coding, modulation, spreading, generation ofan OFDM signal, etc.) on the physical layer. The channel coding,spreading, and the like increase the redundancy of transmitted data.Accordingly, the data amount of a transmitted data stream obtained byperforming the digital signal processing on the physical layer isgenerally larger than that of a data stream before performing thedigital signal processing. For this reason, in the separated structuredisclosed in Patent Literature 1 and Non-Patent Literature 1, trafficcongestion in a communication line between the REC and the RE may occurdue to an increase in traffic in the future. To deal with this, thepresent inventors have studied a modification so as to perform thebaseband signal processing at the RE instead of at the REC. Thissuppresses the traffic congestion in the communication line between theREC and the RE. Further, when a plurality of REs are connected to oneREC, the baseband signal processing is performed in a distributed mannerbetween the REs, thereby making it possible to reduce the processingload of the REC.

However, the modification so as to perform the baseband signalprocessing at the REs instead of at the REC causes another problem.Specifically, when the baseband signal processing is performed atrespective REs, it is difficult to perform cooperative control amongthese REs. A specific example of the cooperative control among the REsis cooperative transmission and reception (e.g., Inter-Cell InterferenceCoordination (ICIC), Coordinated multipoint transmission/reception(CoMP)) between one mobile station and a plurality of cells (or sectors)of the plurality of REs. The CoMP is to be adopted as an LTE-Advancedtechnique that is being standardized by the 3rd Generation PartnershipProject (3GPP). The CoMP is intended to, for example, increase thecommunication speed of mobile stations located at a cell edge, andimprove the cell throughput. In the CoMP, cells or sectors cooperatewith each other to transmit and receive signals to and from one mobilestation. This leads to an improvement of the Signal to Noise Ratio (SNR)and suppression of the inter-cell interference. To carry out the CoMP,it is desirable to perform a radio resource control for a plurality ofcells (or sectors) in a centralized manner. The centralized radioresource control can be achieved relatively easily by performing thebaseband signal processing for the plurality of REs and control of thebaseband signal processing at one REC in a centralized manner.

As described above, for example, the need for reducing the trafficbetween the REC and the RE and the need for achieving the cooperativecontrol among the plurality of REs are conflicting needs in terms of theallocation of the baseband signal processing. In other words, when thebaseband signal processing is performed at the REC or at the RE in afixed manner, one of the above-mentioned needs can be met, but it isdifficult to meet the other need. Additionally, other needs, such as theneed for suppressing power consumption in the REC, conflict with theneed to achieve the cooperative control. Accordingly, it is desirable toappropriately select one of the REC and the RE to perform at least apart of the baseband signal processing, depending on the need to bepreferentially met.

The present invention has been made based on the above-mentioned studyby the present inventors. Therefore, it is an object of the presentinvention to provide a radio station having a separated structure and amethod of processing user data capable of selecting which one of the RECand the RE is used to perform at least a part of baseband signalprocessing for user data.

Solution to Problem

A first aspect of the present invention includes a radio station that isused in a radio communication network and is capable of transmitting andreceiving user data including downlink user data and uplink user data toand from a plurality of mobile stations via an air interface. The radiostation includes a first part and at least one second part that can bearranged so as to be physically separated from the first part and isconnected to the first part via a transmission line so as to be able tocommunicate with the first part.

The first part includes a first scheduling unit and a first signalprocessing unit. The first scheduling unit is configured to performdynamic scheduling to allocate a plurality of radio resources to theplurality of mobile stations or the user data. The first signalprocessing unit is configured to be capable of performing digital signalprocessing in order to transmit the downlink user data to the airinterface and to restore the uplink user data from a signal receivedfrom the air interface.

The second part includes a second signal processing unit and an analogsignal processing unit. The second signal processing unit is configuredto be capable of performing, instead of the first processing unit,digital signal processing for a first mobile station connected to thesecond part. The analog signal processing unit performs analog signalprocessing including at least one of frequency conversion and poweramplification to provide the air interface to the first mobile station.

A second aspect of the present invention includes a method of processinguser data performed by a radio station. The radio station is used in aradio communication network, and is configured to transmit and receiveuser data including downlink user data and uplink user data to and froma plurality of mobile stations via an air interface. The radio stationincludes a first part and at least one second part that can be arrangedso as to be physically separated from the first part and is connected tothe first part via a transmission line so as to be able to communicatewith the first part.

The first part includes a first signal processing unit capable ofperforming digital signal processing in order to transmit the downlinkuser data to the air interface and to restore the uplink user data froma signal received from the air interface. The second part includes asecond signal processing unit capable of performing, instead of thefirst signal processing unit, digital signal processing for a firstmobile station connected to the second part.

The processing method according to the second aspect includesalternatively using one of the first and second signal processing unitsfor the digital signal processing for the first mobile station.

Advantageous Effects of Invention

According to the above-mentioned aspects of the present invention, it ispossible to provide a radio station having a separated structure and amethod of processing user data capable of selecting which one of the RECand the RE is used to perform at least a part of baseband signalprocessing for user data.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration example of a radiobase station according to a first embodiment of the invention;

FIG. 2 is a block diagram showing a configuration example of a radiobase station according to a second embodiment of the invention;

FIG. 3A is a diagram showing a protocol structure and a functionallayout of the radio base station according to the second embodiment ofthe invention;

FIG. 3B is a diagram showing a protocol structure and a functionallayout of the radio base station according to the second embodiment ofthe invention;

FIG. 4 is a block diagram showing a configuration example of a radiobase station according to a third embodiment of the invention;

FIG. 5A is a diagram showing a protocol structure and a functionallayout of the radio base station according to the third embodiment ofthe invention;

FIG. 5B is a diagram showing a protocol structure and a functionallayout of the radio base station according to the third embodiment ofthe invention;

FIG. 6 is a block diagram showing a configuration example of a radiobase station according to a fourth embodiment of the invention;

FIG. 7 is a block diagram showing a configuration example of a radiobase station according to a fifth embodiment of the invention;

FIG. 8 is a sequence diagram showing operation examples of a primaryscheduler and a secondary scheduler according to the fifth embodiment ofthe invention;

FIG. 9 is a sequence diagram showing operation examples of the primaryscheduler and the secondary scheduler according to the fifth embodimentof the invention;

FIG. 10 is a block diagram showing a configuration example of a radiobase station according to a sixth embodiment of the invention;

FIG. 11A is a diagram showing a protocol structure and a functionallayout of the radio base station according to the sixth embodiment ofthe invention;

FIG. 11B is a diagram showing a protocol structure and a functionallayout of the radio base station according to the sixth embodiment ofthe invention;

FIG. 12 is a block diagram showing a configuration example of a radiobase station according to a seventh embodiment of the invention;

FIG. 13A is a diagram showing a protocol structure and a functionallayout of the radio base station according to the seventh embodiment ofthe invention;

FIG. 13B is a diagram showing a protocol structure and a functionallayout of the radio base station according to the seventh embodiment ofthe invention;

FIG. 14 is a block diagram showing a configuration example of a radiobase station according to an eighth embodiment of the invention;

FIG. 15A is a diagram showing a protocol structure and a functionallayout of the radio base station according to the eighth embodiment ofthe invention; and

FIG. 15B is a diagram showing a protocol structure and a functionallayout of the radio base station according to the eighth embodiment ofthe invention.

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the present invention will be described indetail below with reference to the drawings. The same or correspondingcomponents are denoted by the same reference numerals throughout thedrawings, and a repeated description thereof is omitted as needed toclarify the explanation. In the following description, E-UTRA/LTE (LongTerm Evolution) radio base stations will be mainly described. However,such a specific radio communication system is described not to limit thescope of the present invention, but to facilitate understanding of thepresent invention. In other words, those skilled in the art can applythe principle and idea grasped from the embodiments described in detailbelow to various radio communication systems.

First Embodiment

FIG. 1 is a block diagram showing a configuration of a radio basestation 1 according to this embodiment. The radio base station 1 is usedin a radio communication network and is capable of transmitting andreceiving user data including downlink user data and uplink user data toand from a plurality of mobile stations via an air interface. The radiobase station 1 includes a first part, i.e., a radio equipment controller(REC) 1A, and at least one second part, i.e., a radio equipment (RE) 1B.The RE 1B can be arranged so as to be physically separated from the REC1A via a transmission line 40, and is connected to the REC 1A via thetransmission line 40 so as to be able to communicate with the REC 1A.The transmission line 40 may be an electrical transmission line or anoptical transmission line. Alternatively, the transmission line 40 maybe a point-to-point type radio transmission line (e.g., a microwaveradio transmission line). The transmission line 40 may include aplurality of physical transmission lines for bidirectional transmission.As shown in FIG. 1, a plurality of REs 1B may be connected to the REC1A.

Internal interfaces 30 and 31, which are arranged in the REC 1A and theRE 1B, respectively, have layer-2 and layer-1 functions forbidirectional communication via the transmission line 40. Each of theinternal interfaces 30 and 31 may be an electrical interface, an opticalinterface, or a radio interface. For example, an existing transceiver,such as 1000BASE-CX, 1000BASE-SX, 1000BASE-LX, 10GBASE-LX4, or a fibrechannel, may be used as the internal interfaces 30 and 31.

The REC 1A includes a scheduler 20. The scheduler 20 performs dynamicscheduling for the downlink and uplink. In other words, the scheduler 20dynamically allocates a plurality of downlink and uplink radio resourcesto a plurality of mobile stations or user data. The radio resources aredistinguished by time, frequency, or spreading code, or a combinationthereof. For example, in the case of E-UTRA, dynamic scheduling isperformed assuming that each radio resource is a resource block and tworesource blocks within one sub-frame (1 msec) are defined as a minimumunit. One resource block includes 12 subcarriers in a frequency domain,and includes seven OFDM symbols in a time domain.

The dynamic scheduling for the downlink is achieved by selecting data tobe allocated to each radio resource from a buffer (not shown), by usinga scheduling technique such as Proportional Fairness (PF), max-C/I(carrier/interference), or round robin. The buffer temporarily storesthe downlink user data which has arrived from an upper network. Thebuffer may store encrypted bearer data (e.g., Si bearer data)transferred between the upper network and the base station 1.Alternatively, the buffer may store data (e.g., PDCP Protocol Data Units(PDUs), RLC PDUs) obtained by performing the layer-2 processing, such asdata compression (e.g., IP header compression) andsegmentation/concatenation, on the downlink user data. The buffer isprepared, for example, for each mobile station, for each bearer, foreach QoS class, or for each mobile station and each QoS class. The unitin which the buffer is prepared is determined as appropriate dependingon the layout of the buffer, requirements for scheduling (e.g., thepresence or absence of a QoS class, the necessity to secure atransmission rate), or the like.

The dynamic scheduling for the uplink is performed based on, forexample, the reception of a resource allocation request from a mobilestation, or a monitoring result of a data buffer arranged in the mobilestation. The dynamic scheduling for the uplink is achieved bydetermining mobile stations to be allocated to radio resources, by usinga scheduling technique such as PF, max-C/I, or round robin.

Further, in the case of E-UTRA, as a specific example, the dynamicscheduling performed by the scheduler 20 includes selection of a payloadin a radio link control (RLC) sublayer, control of re-transmission in aMAC sublayer, and designation of a coding rate, a modulation scheme anda radio resource in a physical layer. Control information relating tothe dynamic scheduling are sent to a BB unit 11A or 11B by signaling asindicated by dashed lines in FIG. 1.

The REC 1A further includes the BB unit 11A. The BB unit 11A performsdigital baseband signal processing. In other words, the BB unit 11Aperforms digital signal processing for transmitting the downlink userdata to the air interface and for restoring the uplink user data fromthe signal received from the air interface. The digital baseband signalprocessing performed by the BB unit 11A includes, for example, layer-2signal processing and layer-1 (physical layer) signal processing. Thelayer-2 signal processing includes at least one of (i) datacompression/de-compression, (ii) data encryption, (iii) addition/removalof a layer-2 header, (iv) data segmentation/concatenation, and (v)composition/decomposition of a transfer format by datamultiplexing/de-multiplexing. The physical layer signal processingincludes channel coding/decoding and modulation/demodulation.

In the case of E-UTRA, as a specific example, the layer-2 signalprocessing includes processing of the RLC sublayer and the MAC sublayer.The RLC sublayer utilizes a bearer termination unit 10 as an upperprotocol layer. The MAC sublayer utilizes the RLC sublayer as an upperprotocol layer, and utilizes the baseband signal processing on thephysical layer (BB-PHY) as a lower protocol layer. The E-UTRA furtherincludes a PDCP sublayer as an upper sublayer of the RLC sublayer.However, processing (e.g., IP header compression, encryption) in thePDCP sublayer is not essential and may be omitted.

In the case of E-UTRA, the PDCP sublayer plays a role in performingprocessing for reducing the data amount to be transmitted in a mannersuitable for the transmission and reception via the air interface.Specifically, the PDCP sublayer performs IP header compression for thedownlink user data, and IP header de-compression for the uplink userdata. The PDCP sublayer also performs encryption of the user data, andduplication and transfer of the user data so as to reduce a delay inhandover.

The RLC sublayer of the E-UTRA performs segmentation and concatenationand re-transmission control for radio bearer data (PDCP Protocol DataUnits (PDUs)) supplied from the PDCP sublayer. The RLC sublayerprovides, to the PDCP sublayer, a data transfer service using a radiobearer. The RLC sublayer is connected to the MAC sublayer through alogical channel (RLC PDUs).

The MAC sublayer of the E-UTRA performs multiplexing of the logicalchannels (RLC PDUs), and hybrid-ARQ (automatic repeat request)re-transmission. The MAC sublayer generates a transport channel bymultiplexing the logical channels (RLC PDUs). The transmission format(data block size) of the transport channel depends on an instantaneousdata rate. The MAC sublayer is connected to the physical layer throughthe transport channel (MAC PDUs).

In the case of E-UTRA, the physical layer signal processing includes notonly channel coding/decoding and modulation/demodulation, but alsoresource mapping and generation of OFDM symbol data (baseband OFDMsignal) by Inverse Fast Fourier Transform (IFFT), for example.

Next, the RE 1B will be described. The RE 1B includes the BB unit 11Band an RF-PHY unit 13. The BB unit 11B is configured to be capable ofperforming partial processing, for a mobile station connected to the RE1B, of the digital baseband signal processing that can be performed bythe BB unit 11A of the REC 1A, instead of the BB unit 11A, i.e.,alternatively therewith.

The RF-PHY unit 13 is connected to an antenna 14, and performs analog RFsignal processing on the physical layer to provide an air interface toeach mobile station connected to the RE 1B. The signal processingperformed by the RF-PHY unit 13 includes at least one of D/A conversion,A/D conversion, frequency up-conversion, frequency down-conversion, andamplification. The RF-PHY unit 13 is selectively coupled to the BB unit11A or 11B. Specifically, the RF-PHY unit 13 receives modulation symboldata (or OFDM symbol data) from the BB unit 11A or 11B, generates adownlink RF signal, and transmits the downlink RF signal via the antenna14. The RF-PHY unit 13 receives an uplink RF signal from the antenna 14,generates a baseband reception signal stream, and supplies the basebandreception signal stream to the BB unit 11A or 11B.

The radio base station 1 alternatively uses one of the BB units 11A and11B for digital baseband signal processing for the user data pertainingto a mobile station connected to the RE 1B. The selection of one of theBB units 11A and 11B to be used may be collectively performed for alluser data pertaining to all mobile stations connected to the radio basestation 1. Alternatively, the selection may be individually performedfor each mobile station, for each user data, or for each bearer (e.g.,an S1 bearer) encrypted between the upper network and the radio basestation 1. When a plurality of REs 1B are connected to the base station1, the selection of one of the BB units 11A and 11B to be used may beindividually performed for each RE 1B.

The selection of one of the BB units 11A and 11B to be used may beperformed through manual setting of the radio base station 1 by anoperator. Alternatively, the selection may be autonomously performed bya controller (not shown), which is arranged in the REC 1A or the RE 11B,by determining the establishment of a selection condition. In one morealternative, the selection may be performed based on an instruction froman external device, such as a resource control apparatus or an OAM(Operation Administration and Maintenance) system, which are arrangedoutside of the radio base station 1.

Next, conditions for selecting one of the BB units 11A and 11B will bedescribed. The selection of one of the BB units 11A and 11B to be usedcan be performed based on various selection conditions. A selectioncondition to be used may be determined as appropriate depending on theneeds to be preferentially met, such as the achievement of thecooperative control among the plurality of REs, the reduction in theprocessing load of the REC, or the reduction in the traffic between theREC and the RE. Specific examples of selection conditions for the BBunits 11A and 11B are given below.

Specific Example 1

The selection of one of the BB units 11A and 11B to be used is performedbased on the amount of traffic to be processed by the entire radio basestation 1, the REC 1A, or the RE 1B. For example, when the amount oftraffic to be processed by the RE 1B exceeds a predetermined level, theBB unit 11A of the REC 1A may be selected. By preferentially using theBB unit 11A of the REC 1A, the cooperative transmission and reception(e.g., CoMP) between one mobile station and a plurality of cells (orsectors) of a plurality of REs 1B can be performed relatively easily,and the cell throughput can be increased. On the other hand, when theamount of traffic to be processed by the RE 1B is less than thepredetermined level, the BB unit 11B of the RE 1B may be selected. As aresult, a redundancy due to channel coding can be avoided and the amountof traffic between the REC and the RE can be reduced. A reduction inpower consumption of the REC 1A can also be expected.

Specific Example 2

The selection of one of the BB units 11A and 11B to be used is performedbased on the necessity to perform a cooperative control among aplurality of REs 1B connected to the REC 1A. For example, when it isnecessary to preferentially perform the cooperative control among theplurality of REs 1B, the BB unit 11A of the REC 1A may be selected. Thismakes it possible to relatively easily perform the cooperativetransmission and reception (e.g., CoMP). On the other hand, when thereis no need to perform the cooperative control among the plurality of REs1B, or when a higher priority is placed on another condition (e.g., areduction in power consumption of the REC 1A, or a reduction in trafficbetween the REC and the RE), the BB unit 11B of the RE 1B may beselected. This makes it possible to meet another need, such as areduction in power consumption of the REC 1A, when there is no need forthe cooperative transmission and reception.

Specific Example 3

The selection of one of the BB units 11A and 11B to be used is performedbased on the power consumption of the entire radio base station 1, theREC 1A, or the RE 1B. For example, when the power consumption of the REC1A exceeds a predetermined level, the BB unit 11B of the RE 1B may beselected. This makes it possible to reduce the power consumption of theREC 1A. Further, for example, when the power consumption of the RE 1Bexceeds the predetermined level, the BB unit 11A of the REC 1A may beselected. This makes it possible to reduce the power consumption of theRE 1B.

Specific Example 4

The selection of one of the BB units 11A and 11B to be used is performedbased on the load status of the REC 1A or the RE 1B. For example, whenthe load of the REC 1A exceeds a predetermined level, the BB unit 11B ofthe RE 1B may be selected. This makes it possible to achieve adistribution of the load between the REC 1A and the RE 1B and suppressan increase in the load of the REC 1A. Further, for example, when theload of the RE 1B exceeds the predetermined level, the BB unit 11A ofthe REC 1A may be selected. This makes it possible to suppress anincrease in the load of the RE 1B. More specifically, a resource userate of each RE 1B (each cell) is measured periodically, and when theresource use rate exceeds the predetermined level, the BB unit 11A ofthe REC 1A may be selected. Alternatively, in the case of setting a newbearer, the resource use rate of the RE 1B may be determined, and whenthe resource use rate exceeds the predetermined level, the BB unit 11Aof the REC 1A may be selected.

Specific Example 5

The selection of one of the BB units 11A and 11B to be used is performedbased on the processing capacity of the REC 1A or the RE 1B. Forexample, when the processing capacity of the RE 1B is less than apredetermined level, the BB unit 11A of the REC 1A may be selected. Thisselection condition is effective when the processing capacity of the BBunit 11B is smaller than that of the BB unit 11A. Since the amount oftraffic to be processed by the RE 1B varies depending on theinstallation location of the RE 1B, the processing capacity required forthe RE 1B also varies. Accordingly, when the RE 1B is arranged at a hightraffic location and the processing capacity of the BB unit 11B is notsufficient, the BB unit 11A of the REC 1A may be selected.

Specific Example 6

The selection of one of the BB units 11A and 11B to be used is performedbased on a power supply status with respect to the REC 1A. For example,when a charging status of a battery which supplies power to the REC 1A,i.e., a charge amount or a charged percentage, exceeds a predeterminedlevel, the BB unit 11A of the REC 1A may be selected. On the other hand,when the charging status of the battery which supplies power to the REC1A is less than the predetermined level, the BB unit 11B of the RE 1Bmay be selected.

Specific Example 7

The selection of one of the BB units 11A and 11B to be used is performedbased on a power supply status with respect to the RE 1B. For example,when the RE 1B can be supplied with power from a power generating devicecapable of self-generation, such as photovoltaic power generation orwind power generation, the BB unit 11B of the RE 1B may be selected.

Specific Example 8

The selection of one of the BB units 11A and 11B to be used is performedbased on a security level or a QoS class of user data. Specifically, theBB unit 11B of the RE 1B may be selected for bearers requiring a highsecurity level and for bearers to which a high QoS class is set, and theBB unit 11A of the REC 1A may be selected for the other bearers. In thiscase, it is preferable that a termination point of a bearer (e.g., an S1bearer) encrypted between the upper network and the radio base station 1be selectable between the REC 1A and the RE 1B.

The specific examples 1 to 8 of the selection conditions described aboveare illustrated by way of example only, and other selection conditionsmay also be used, as a matter of course. Further, the specific examples1 to 8 of the selection conditions described above and other optionalselection conditions can be combined as appropriate and used.

As described above, the BB units 11A and 11B are alternatively used fordigital baseband signal processing for the user data pertaining to amobile station connected to the RE 1B. The signal processing performedby the BB units 11A and 11B may be a part of the entire layer-2 andlayer-1 (physical layer) digital signal processing to be performed onthe user data. In this case, the other baseband signal processing, whichis not performed by the BB unit 11A and the BB unit 11B, is performed byother signal processing units (not shown).

For example, the REC 1A and the RE 1B each may be equipped with a BB-PHYunit that performs baseband signal processing (e.g., channelcoding/decoding and modulation/demodulation) on the physical layer, andone of the BB-PHY units may be alternatively used. The BB-PHY unitscorrespond to the BB units 11A and 11B. In this case, the REC 1A may beequipped with a layer-2 unit that performs baseband signal processing(e.g., processing of the RLC sublayer and the MAC sublayer) for thelayer-2, and the layer-2 unit may perform the layer-2 processingrelating to the plurality of REs 1B in a centralized manner. Suchmodifications will be described in the following second to eighthembodiments.

Although not shown in FIG. 1, the layout of a function for terminating abearer established with the upper network can be modified in variousmanners. Further, the layout of the buffer referred to by the scheduler20 for dynamic scheduling of the downlink can also be modified invarious manners. In other words the bearer termination function and thebuffer can be appropriately distributed between the REC 1A and the RE1B. Various additional effects can be obtained by adjusting the layoutof these functional units. Various aspects of the layout of thesefunctional units will be described in the following second to eighthembodiments.

As described above, the radio base station 1 according to thisembodiment includes the BB units 11A and 11B, and is configured toselect one of the BB units 11A and 11B for digital baseband signalprocessing for user data pertaining to each mobile station connected tothe RE 1B. Accordingly, the radio base station 1 can select which one ofthe REC 1A and the RE 1B is used to perform at least a part of thebaseband signal processing, depending on the need to be preferentiallymet among a plurality of needs, such as a need for reducing the amountof traffic between the REC and the RE, and a need for achieving acooperative control among a plurality of REs 1B.

Second Embodiment

FIG. 2 is a block diagram showing a configuration example of a radiobase station 2 according to this embodiment. The radio base station 2includes a first part, i.e., a radio equipment controller (REC) 2A, andat least one second part, i.e., a radio equipment (RE) 2B. Though onlyone RE 2B is illustrated in FIG. 2, a plurality of REs 2B may beconnected to the REC 2A as shown in FIG. 1. The radio base station 2differs from the above-described radio base station 1 in that bearertermination units 10A and 10B are arranged in the REC 2A and the RE 2B,respectively. The bearer termination units 10A and 10B can terminate abearer established between the upper network (e.g., RNC of UMTS, EPC ofE-UTRA) and the base station 2 so as to transfer user data. In general,a bearer (e.g., an S1 bearer of E-UTRA) for transferring user data isencrypted with a tunneling protocol (e.g., IPsec). A bearer isestablished for each data flow (e.g., a Packet Data Network (PDN)connection of E-UTRA) between each mobile station and an externalnetwork. Accordingly, the bearer termination units 10A and 10B canterminate a plurality of encrypted bearers between the upper network andthe base station 2, receive the downlink user data pertaining to aplurality of mobile stations from the upper network, and send the uplinkuser data pertaining to the plurality of mobile stations to the uppernetwork.

Further, the radio base station 2 is configured to select terminationpoints of a plurality of bearers between the REC 2A and the RE 2B. Oneof the bearer termination units 10A and 10B to be used may be determinedin accordance with the selection of one of the BB units 11A and 11B tobe used. In other words, when the BB unit 11A of the REC 2A is used forthe digital baseband signal processing for the user data, the bearertermination unit 10A is used for the bearer termination. On the otherhand, when the BB unit 11B of the RE 2B is used for the digital basebandsignal processing, the bearer termination unit 10B is used for thebearer termination.

When the bearer is terminated in the RE 2B, the radio base station 2transfers the encrypted bearer data (e.g., S1 bearer data) via thetransmission line 40 from the REC 2A to the RE 2B. This allows the radiobase station 2 to enhance security between the REC 2A and the RE 2B. Asdescribed above, the RE 2B is expected to be arranged at a remotelocation that is easily accessed by a third party. Transmission of theencrypted bearer data, instead of the user data, makes it possible toprotect the user data against unauthorized access.

The selection between the bearer termination units 10A and 10B, that is,the selection of a bearer termination point, can be performed inaccordance with, for example, “specific example 8” of the selectionconditions described above. In this case, a termination point may beindividually selected for each bearer. Specifically, bearers requiring ahigh security level and bearers to which a high QoS class is set may beterminated in the RE 2B. The other bearers may be terminated in the REC2A. The selection between the bearer termination units 10A and 10B, aswell as the selection between the BB units 11A and 11B, may be performedbased on at least one of the other specific examples 1 to 7.

Alternatively, for example, bearer termination points may be selectedbased on the security level of the transmission line 40 between the REC2A and the RE 2B. Specifically, when the security level of thetransmission line 40 is relatively high, the bearers may be terminatedin the REC 2A, and when the security level of the transmission line 40is relatively low, the bearers may be terminated in the RE 2B. The casewhere the security level of the transmission line 40 is relatively highis, for example, when the transmission line 40 is a dedicated line of atelecom carrier, or when the transmission line 40 is laid on thepremises managed by the telecom carrier. The case where the securitylevel of the transmission line 40 is relatively low is, for example,when the transmission line 40 is a general public line, or when thetransmission line 40 is laid in a place that is not under full control.

Bearer termination points may be selected at the time of setting up theradio base station 2. Alternatively, bearer termination points may beselected according to switching of the transmission line 40, forexample, switching between a main transmission line and a backuptransmission line. Specifically, a controller 50 arranged in the radiobase station 2 may switch termination points according to the respectivesecurity levels of the main transmission line and the backuptransmission line when the main transmission line and the backuptransmission line have different security levels. The switching ofbearer termination points may be performed according to an instructionfrom an external device (e.g., a resource control device or an OAMsystem), instead of the controller 50.

Next, a layout of a buffer 21 shown in FIG. 2 will be described. Thebuffer 21 temporarily stores the downlink user data which has arrivedfrom the upper network, and is referred to by the scheduler 20 for thedynamic scheduling. In the configuration example of FIG. 2, the buffer21 is arranged in the REC 2A. Accordingly, the buffer 21 shown in FIG. 2may store the encrypted bearer data for each mobile station, for eachbearer, for each QoS class, or for each mobile station and each QoSclass. However, as described in detail in the first embodiment, such alayout of the buffer 21 is illustrated by way of example only. Thebuffer 21 may be arranged between the bearer termination unit 10A andthe BB unit 11A.

The buffer 21 may be arranged so as to store the user data streamobtained by performing the data compression and encryption in thelayer-2. In the case of E-UTRA, the user data stream obtained byperforming the data compression and encryption in the layer-2corresponds to the PDCP Protocol Data Units (PDUs), which are a datastream obtained after the PDCP sublayer is processed (i.e., radio bearerdata). Alternatively, the buffer 21 may be arranged so as to store theuser data stream obtained by performing segmentation/concatenation andaddition of a layer-2 header in the layer-2. In the case of E-UTRA, theuser data stream obtained by performing the segmentation/concatenationand addition of a layer-2 header corresponds to the RLC PDUs, which area data stream obtained after the Radio-Link Control (RLC) sublayer isprocessed (i.e., a logical channel). In such cases, the buffer 21 may bearranged in each of the REC 2A and the RE 2B and may be used inaccordance with the selection between the BB units 11A and 11B.

The scheduler 20, however, needs to recognize the storage status of thebuffer 21 during the dynamic scheduling for the downlink. Accordingly,both the buffer 21 and the scheduler 20 are arranged in the REC 2A,thereby facilitating the dynamic scheduling. Moreover, the amount ofcontrol data to be transferred between the internal interfaces 30 and 31can be reduced. The REC 2A (the internal interface 30) may selectivelytransmit data selected by the scheduler 20 from the downlink user dataor from the data stream including the downlink user data stored in thebuffer 21.

The radio base station 2 is configured to select one of the BB units 11Aand 11B to be used. Accordingly, the radio base station 2 can selectwhich one of the REC 2A and RE 2B is used to perform at least a part ofthe baseband signal processing, depending on the need to bepreferentially met among the plurality of needs, as in the radio basestation 1.

Further, in this embodiment, when the BB unit 11B is used, the bearertermination is also performed at the RE 2B. Accordingly, the use of thebearer termination unit 10B and the BB unit 11B allows the radio basestation 2 to enhance the security of the transmission line 40. On theother hand, when a reduction in the amount of traffic between the RECand the RE should be met in priority to the enhancement of the securityof the transmission line 40, the radio base station 2 can meet the needby using the bearer termination unit 10A and the BB unit 11A.

FIGS. 3A and 3B show the details of the functional layout in the radiobase station 2 regarding the downlink transmission of user data in theE-UTRA. The functional layout shown in FIG. 3A corresponds to the casewhere the bearer termination unit 10A and the BB unit 11A of the REC 2Aare used in the configuration example of FIG. 2. On the other hand, thefunctional layout shown in FIG. 3B corresponds to the case where thebearer termination unit 10B and the BB unit 11B of the RE 2B are used.In FIGS. 3A and 3B, the BB units 11A and 11B each include threesub-units related to the layer-2 processing, i.e., a PDCP unit 110, anRLC unit 111, and a MAC unit 112. The PDCP unit 110 performs processingon the PDCP sublayer. The RLC unit 111 performs processing on the RLCsublayer. The MAC unit 112 performs processing on the MAC sublayer. TheBB units 11A and 11B each further include four sub-units related to thebaseband physical layer (BB-PHY) processing, i.e., a coding unit 120, amodulation unit 121, a resource mapping unit 122, and an IFFT unit 123.The RF-PHY unit 13 includes an up-converter 130 and an amplifier 131. Inthe example of FIG. 3A, the OFDM symbol data (baseband OFDM signal) istransferred from the REC 2A to the RE 2B. In the example of FIG. 3B, theS1 bearer data is transferred from the REC 2A to the RE 2B.

Third Embodiment

FIG. 4 is a block diagram showing a configuration example of a radiobase station 3 according to this embodiment. The radio base station 3includes a first part, i.e., a radio equipment controller (REC) 3A, andat least one second part, i.e., a radio equipment (RE) 3B. Though onlyone RE 3B is illustrated in FIG. 4, a plurality of REs 3B may beconnected to the REC 3A as shown in FIG. 1. The radio base station 3differs from the above-described radio base station 1 in that the bearertermination unit 10 is arranged in the REC 3A. The bearer terminationunit 10 terminates a bearer, which is established between the uppernetwork (e.g., RNC of UMTS, EPC of E-UTRA) and the base station 3, so asto transfer user data.

In the example of FIG. 4, the buffer 21 is arranged between the bearertermination unit 10 and the BB units 11A and 11B. Accordingly, thebuffer 21 stores the user data (e.g., IP packets) itself beforeperforming data compression, encryption, segmentation and multiplexingin the layer-2 processing. However, such a layout of the buffer 21 isillustrated by way of example only.

In FIG. 4, the REC 3A may be configured to perform processing (e.g., IPheader compression, encryption) on the PDCP sublayer at the bearertermination unit 10. In this case, the BB units 11A and 11B may performother baseband signal processing (i.e., processing of RLC and MACsublayers, and BB-PHY processing) except for the PDCP sublayer. In thiscase, the buffer 21 may store the PDCP PDUs for each mobile station, foreach bearer, for each QoS class, or for each mobile station and each QoSclass.

The radio base station 3 is configured to select one of the BB units 11Aand 11B to be used. Accordingly, the radio base station 3 can selectwhich one of the REC 3A or the RE 3B is used to perform at least a partof the baseband signal processing, depending on the need to bepreferentially met among the plurality of needs, as in the radio basestation 1.

Furthermore, in contrast to the second embodiment described above, theREC 3A performs the bearer termination even when the BB unit 11B of theRE 3B is used. Accordingly, the header added to the encrypted bearerdata (e.g., S1 bearer data) can be reduced. This leads to a reduction inthe data amount to be transferred between the REC 3A and the RE 3B, ascompared with the case of transmitting the bearer data to the RE 3B.

FIGS. 5A and 5B show the details of the functional layout in the radiobase station 3 regarding the downlink transmission of user data in theE-UTRA. The functional layout shown in FIG. 5A corresponds to the casewhere the BB unit 11A of the REC 3A is used in the configuration exampleof FIG. 4. On the other hand, the functional layout shown in FIG. 5Bcorresponds to the case where the BB unit 11B of the RE 3B is used. Inthe example of FIG. 5A, the OFDM symbol data (baseband OFDM signal) istransferred from the REC 3A to the RE 3B. In the example of FIG. 5B, theuser data is transferred from the REC 3A to the RE 3B.

Fourth Embodiment

FIG. 6 is a block diagram showing a configuration example of a radiobase station 4 according to this embodiment. The configuration exampleshown in FIG. 6 is a modification of the radio base station 3 shown inFIG. 4. The radio base station 4 includes a first part, i.e., a radioequipment controller (REC) 4A, and at least one second part, i.e., aradio equipment (RE) 4B. Though only one RE 4B is illustrated in FIG. 6,a plurality of REs 5B may be connected to the REC 4A as shown in FIG. 1.The radio base station 4 differs from the radio base station 3 shown inFIG. 4 in that the REC 4A includes a handover (HO) control unit 51. Theconfiguration and functional layout of the RE 4B are the same as thoseof the RE 3B shown in FIGS. 4, 5A, and 5B.

When a mobile station communicating over an air interface performshandover to another base station (target base station), the HO controlunit 51 transfers the downlink user data pertaining to the mobilestation held in the buffer 21, or the data stream including the downlinkuser data, to the target base station. The transfer of the user data tothe target base station is performed in the same manner as in a typicalhandover procedure. Specifically, the user data may be transferred tothe target base station by using an interface (e.g., an X2 interface)available between base stations, or may be transferred via an uppernetwork.

In FIG. 6, the REC 4A may be configured to perform processing (e.g., IPheader compression, encryption) on the PDCP sublayer at the bearertermination unit 10. In this case, the BB units 11A and 11B may performother baseband signal processing (i.e., processing of RLC and MACsublayers, and BB-PHY processing) except for the PDCP sublayer. In thiscase, the buffer 21 may store the PDCP PDUs for each mobile station, foreach bearer, for each QoS class, or for each mobile station and each QoSclass.

In the configuration example shown in FIG. 6, the REC 4A buffers theuser data or the data stream (e.g., PDCP PDUs) containing the user data,thereby facilitating the data transfer to the target base station duringthe handover. In other words, there is no need to transfer the data fromthe RE 4B to the REC 4A during the handover. When a mobile station movesbetween REs 4B connected to the REC 4A, it is only necessary for the REC4A to change the transmission destination of the buffered user data orthe data stream (e.g., PDCP PDUs) containing the user data to the RE 4Bas the handover target. This makes it possible to easily providecontinuous services by following the movement of a mobile station.

Fifth Embodiment

FIG. 7 is a block diagram showing a configuration example of a radiobase station 5 according to this embodiment. The configuration exampleshown in FIG. 7 is a modification of the radio base station 3 shown inFIG. 4. The radio base station 5 includes a first part, i.e., a radioequipment controller (REC) 5A, and at least one second part, i.e., aradio equipment (RE) 5B. Though only one RE 5B is illustrated in FIG. 7,a plurality of REs 5B may be connected to the REC 5A as shown in FIG. 1.The radio base station 5 differs from the radio base station 3 shown inFIG. 4 in that the REC 5A includes a primary scheduler 20A and the RE 5Bincludes a secondary scheduler 20B.

In the radio base station 5, the primary scheduler 20A is arranged inthe REC 5A. Accordingly, the radio base station 5 can performcooperative scheduling at the REC 5A, as in the radio base station 1.Further, in this embodiment, the secondary scheduler 20B performs a partof the processing related to dynamic scheduling. The secondary scheduler20B operates in a cooperative manner with the primary scheduler 20A forthe dynamic scheduling. Specific examples of dividing the functionsbetween the primary scheduler 20A and the secondary scheduler 20B willbe described below.

In a first example, the secondary scheduler 20B calculates a parameterused for dynamic scheduling based on the radio communication quality ofthe air interface, and sends the parameter to the primary scheduler 20A.The main scheduling techniques, such as PF scheduling and Max-C/Ischeduling, use the radio communication quality of the air interface.For example, PF scheduling uses, as a parameter, a ratio between aninstantaneous predicted radio communication quality and a previousaverage radio communication quality of a mobile station so as to securethe fairness of transmission opportunities among mobile stations. Thisparameter is called a PF metric. Examples of the radio communicationquality used for calculation of the PF metric include a data rate and asignal-to-interference ratio (SINR). The PF metric is calculated as, forexample, a ratio between an instantaneous SINR and an average SINR(i.e., instantaneous SINR/average SINR).

The secondary scheduler 20B calculates a parameter, such as the PFmetric, using the radio communication quality, thereby reducing theprocessing load of the primary scheduler 20A. Further, the data amountto be transmitted from the RE 5B to the REC 5A by using the transmissionline 40 can be reduced. In the case of calculating a parameter (e.g., PFmetric) in the REC 5A, it is necessary to send the measurement resultsof the current and previous radio communication qualities from the RE 5Bto the REC 5A. However, when the secondary scheduler 20B calculates aparameter, only the calculated parameter may be sent instead of themeasurement results of the current and previous radio communicationqualities.

FIG. 8 is a sequence diagram showing operations of the primary scheduler20A and the secondary scheduler 20B when the secondary scheduler 20Bcalculates the PF metric. In step S11, a mobile station (UE) sendsquality information. This quality information indicates the downlinkradio communication quality measured by the mobile station. In step S12,the secondary scheduler 20B calculates the PF metric by using thequality information received from the mobile station. In step S13, thesecondary scheduler 20B sends the PF metric to the primary scheduler20A. In step S14, the primary scheduler 20A executes dynamic schedulingby using the PF metric received from the secondary scheduler 20B, anddetermines mobile stations or user data to be allocated to downlinkradio resources.

Next, a second example of dividing the functions between the primaryscheduler 20A and the secondary scheduler 20B will be described. In thesecond example, the secondary scheduler 20B executes scheduling forH-ARQ re-transmission or scheduling for re-transmission of the RLCsublayer. Specifically, the secondary scheduler 20B buffers the downlinktransmitted data, and when the mobile station requests re-transmission,the secondary scheduler 20B performs re-transmission based on are-transmission instruction from the primary scheduler 20A. For example,the secondary scheduler 20B may allocate, for the re-transmission, thesame radio resource as that used for the transmission immediatelybefore. This contributes to a reduction in the processing load of theprimary scheduler 20A. Further, since there is no need to transfer there-transmitted data from the REC 5A to the RE 5B, the data amount to betransmitted via the transmission line 40 can be reduced.

FIG. 9 is a sequence diagram showing operations of the primary scheduler20A and the secondary scheduler 20B when the secondary scheduler 20Bcontrols re-transmission. In step S21, the secondary scheduler 20Bbuffers the downlink transmitted data. In step S22, the mobile stationsends a re-transmission request (e.g., NACK), and the primary scheduler20A receives the re-transmission request. In step S23, the primaryscheduler 20A instructs the secondary scheduler 20B to performre-transmission. In step S24, the secondary scheduler 20B performsre-transmission according to the instruction from the primary scheduler20A.

As is apparent from the descriptions of the first to fourth embodiments,the functional layout shown in the configuration example of FIG. 7 isillustrated by way of example only. For example, as described in thesecond embodiment, the bearer termination units 10 (10A and 10B) may bearranged in the REC 5A and the RE 5B, and one of them may bealternatively used. Further, the PDCP processing may be performed by thebearer termination units 10. Furthermore, the buffer 21 may be arrangedon the upper network side relative to the bearer termination units 10.

Sixth Embodiment

The first to fifth embodiments illustrate examples in which the RECexecutes dynamic scheduling, regardless of which one of the REC and theRE plays a role in performing the digital baseband signal processing.Thus, the REC can perform cooperative scheduling in a centralized mannerin consideration of the radio resources necessary for respective REs 1B.Accordingly, the radio base stations 1 to 5 can easily perform thecooperative control between cells, as compared with the case ofperforming scheduling in a distributed manner in the respective REs 1B.On the other hand, this embodiment illustrates an example in which theRE performs dynamic scheduling when the BB unit 11B is used for thedigital baseband signal processing for user data.

FIG. 10 is a block diagram showing a configuration example of a radiobase station 6 according to this embodiment. The radio base station 6includes a first part, i.e., a radio equipment controller (REC) 6A, andat least one second part, i.e., a radio equipment (RE) 6B. Though onlyone RE 6B is illustrated in FIG. 10, a plurality of REs 6B may beconnected to the REC 6A as shown in FIG. 1. The REC 6A includes a firstscheduler 20C and a buffer 21A. The RE 6B includes a second scheduler20D and a buffer 21B.

Each of the first scheduler 20C and the second scheduler 20D can performdynamic scheduling for the downlink and uplink. The processing capacityof the second scheduler 20D may be smaller than that of the firstscheduler 20C. This is because the first scheduler 20C should performscheduling for a number of mobile stations connected to a plurality ofREs 6B, whereas the second scheduler 20D only needs to performscheduling for mobile stations connected to a single RE 6B.

The second scheduler 20D is capable of performing dynamic scheduling formobile stations connected to the RE 6B, instead of the first scheduler20C. The radio base station 6 is configured to select which one of thefirst scheduler 20C and the second scheduler 20D is used to performdynamic scheduling for mobile stations connected to the RE 6B. Theselection may be individually performed for each RE 6B, or may becollectively performed for a plurality of REs 6B connected to the REC6A. When the first scheduler 20C executes dynamic scheduling, the buffer21A and the BB unit 11A of the REC 6A are used. On the other hand, whenthe second scheduler 20D executes dynamic scheduling, the buffer 21B andthe BB unit 11B of the RE 6B are used.

When the radio base station 6 requires, for example, the cooperativetransmission and reception (e.g., CoMP) between a plurality of REs 6Band one mobile station, the first scheduler 20C, the buffer 21A, and theBB unit 11A of the REC 6A may be used for the dynamic scheduling.Therefore, the REC 6A can control the radio resources in a centralizedmanner for the plurality of REs 6B, thereby making it possible torelatively easily perform the cooperative transmission and reception(e.g., CoMP).

On the other hand, the radio base station 6 does not require thecooperative transmission and reception (e.g., CoMP) between a pluralityof REs 6B and one mobile station, the second scheduler 20D, the buffer21B, and the BB unit 11B of each RE 6B may be used for the dynamicscheduling. This leads to a reduction in the amount of traffic betweenthe REC and the RRH. This also contributes to a reduction in powerconsumption of the REC 6A.

FIGS. 11A and 11B show the details of the functional layout in the radiobase station 6 regarding the downlink transmission of user data in theE-UTRA. The functional layout shown in FIG. 11A corresponds to the casewhere the first scheduler 20C, the buffer 21A, and the BB unit 11A ofthe REC 6A are used in the configuration example of FIG. 10. On theother hand, the functional layout shown in FIG. 11B corresponds to thecase where the second scheduler 20D, the buffer 21B, and the BB unit 11Bof the RE 6B are used. In the example of FIG. 11A, the OFDM symbol data(baseband OFDM signal) is transferred from the REC 6A to the RE 6B. Inthe example of FIG. 11B, the user data is transferred from the REC 6A tothe RE 6B.

The second scheduler 20D may be configured to be capable of performingonly a part of the dynamic scheduling for mobile stations connected tothe RE 1B, instead of performing the whole dynamic scheduling. Forexample, the first scheduler 20C may determine a range of radioresources that can be allocated to mobile stations connected to the RE1B. In this case, the second scheduler 20D may dynamically allocate theresources to the mobile stations from the range of radio resourcesdetermined by the first scheduler 20C. Alternatively, for example, as inthe configurations of the primary scheduler and the secondary schedulerdescribed in the fifth embodiment, the first scheduler 20C may performdynamic scheduling except for H-ARQ re-transmission, and the scheduler20D may perform scheduling for the H-ARQ re-transmission. Furthermore,the second scheduler 20D may calculate a parameter used for dynamicscheduling based on the radio communication quality of the airinterface, and may send the parameter to the first scheduler 20C. Inthis case, the first scheduler 20C may perform dynamic scheduling byusing the parameter calculated by the second scheduler 20D.

Seventh Embodiment

As described above in the first embodiment, the digital basebandprocessing functions, which are arranged in both the REC and the RE, andone of which is alternatively used, may be a part of the layer-2 andphysical layer digital signal processing to be performed on user data.This embodiment illustrates an example in which digital signalprocessing functions for the physical layer are arranged in both the RECand the RE.

FIG. 12 is a block diagram showing a configuration example of a radiobase station 7 according to this embodiment. The radio base station 7includes a first part, i.e., a radio equipment controller (REC) 7A, anda second part, i.e., a radio equipment (RE) 7B. In the configurationexample of FIG. 12, the REC 7A and the RE 7B include BB-PHY units 124Aand 124B, respectively. The REC 7A further includes a unit that performslayer-2 signal processing. More specifically, since FIG. 12 shows aspecific example of the E-UTRA, the REC 7A includes the PDCP unit 110,the RLC unit 111, and the MAC unit 112.

The BB-PHY units 124A and 124B perform digital baseband signalprocessing for the physical layer. More specifically, the signalprocessing performed by the BB-PHY units 124A and 124B includes channelcoding and modulation for transmitting the downlink user data to the airinterface. The signal processing performed by the BB-PHY unit 12 alsoincludes demodulation and channel decoding for restoring the uplink userdata from the signal received from the air interface. The channel codingand decoding includes, for example, block coding or convolutionalcoding, or a combination thereof. The channel coding and decoding by theBB-PHY units 124A and 124B are performed by using, for example, a codingalgorithm such as turbo code, Viterbi code, or Reed-Solomon code.Depending on the communication system, the signal processing performedby the BB-PHY units 124A and 124B may include, for example,spreading/de-spreading, resource mapping, and generation of an OFDMsignal involving Inverse Fast Fourier Transform (IFFT).

The radio base station 7 according to this embodiment is configured toselect one of the BB-PHY units 124A and 124B to be used. Accordingly,the radio base station 7 can select which one of the REC 7A and the RE7B is used to perform the digital baseband signal processing for thephysical layer, depending on the need to be preferentially met among theplurality of needs, such as the need for reducing the amount of trafficbetween the REC and the RE, and the need for achieving the cooperativecontrol among the plurality of REs.

When the BB-PHY unit 124B of the RE 7B is used, the data stream thatcontains the user data and is transmitted through the transmission line40 does not include redundant data generated as a result of channelcoding (e.g., block coding, convolutional coding, or turbo coding).Accordingly, the radio base station 7 can suppress the data amount to betransmitted between the REC 7A and the RE 7B. Further, even when theBB-PHY unit 124B of the RE 7B is used, the digital signal processing canbe performed in a distributed manner between the REC 7A and the RE 7B,because the layer-2 signal processing function is placed in the REC 7A.Furthermore, according to this embodiment, layer-2 unit (i.e., the PDCPunit 110, the RLC unit 111, and the MAC unit 112) which is arranged inthe REC 7A can be shared for processing the user data pertaining to theplurality of REs 7B. Therefore, these layer-2 units can be effectivelyused.

On the other hand, when the BB-PHY unit 124A of the REC 7A is used, theradio base station 7 can relatively easily perform the cooperativetransmission and reception (e.g., CoMP). This is because it is onlynecessary for the scheduler 20 to control the RLC unit 111, the MAC unit112, and the BB-PHY unit 124A, which are arranged in the REC 7A, uponexecution of dynamic scheduling.

FIGS. 13A and 13B show the details of the functional layout in the radiobase station 7 regarding the downlink transmission of user data in theE-UTRA. The functional layout shown in FIG. 13A corresponds to the casewhere the BB-PHY unit 124A of the REC 7A is used in the configurationexample of FIG. 12. On the other hand, the functional layout shown inFIG. 13B corresponds to the case where the BB-PHY unit 124B of the RE 7Bis used. In the example of FIG. 13A, the OFDM symbol data (baseband OFDMsignal) is transferred from the REC 7A to the RE 7B. In the example ofFIG. 13B, the MAC-PDU (i.e., a transport channel) is transferred fromthe REC 7A to the RE 7B.

In the example shown in FIGS. 12, 13A, and 13B, the buffer 21 isarranged between the RLC unit 111 and the MAC unit 112. Accordingly, thebuffer 21 may store the RLC PDUs (i.e., a logical channel) for eachmobile station, for each bearer, for each QoS class, or for each mobilestation and each QoS class. However, as described in detail in the firstembodiment, the layout of the buffer 21 can be changed as needed. Forexample, the buffer 21 may be arranged between the PDCP unit 110 and theRLC unit 111.

Eighth Embodiment

This embodiment illustrates an example in which the layer-2 signalprocessing to be performed on user data is allocated to both the REC andthe RE, and the physical layer signal processing to be performed on userdata is allocated only to the RE.

FIG. 14 is a block diagram showing a configuration example of a radiobase station 8 according to this embodiment. The radio base station 8includes a first part, i.e., a radio equipment controller (REC) 8A, anda second part, i.e., a radio equipment (RE) 8B. In the configurationexample of FIG. 14, the REC 8A and the RE 8B include layer-2 units 113Aand 113B, respectively. The RE 8B further includes a BB-PHY unit 124.

The layer-2 units 113A and 113B perform the layer-2 signal processingexcept for dynamic scheduling. The layer-2 signal processing includes atleast one of (i) data compression/de-compression, (ii) data encryption,(iii) addition/removal of a layer-2 header, datasegmentation/concatenation, and (v) composition/decomposition of atransfer format by data multiplexing/de-multiplexing. In the case ofE-UTRA, as a specific example, the layer-2 signal processing includesprocessing of the RLC sublayer and the MAC sublayer. The E-UTRA furtherincludes a PDCP sublayer as an upper sublayer of the RLC sublayer.However, processing (e.g., IP header compression, encryption) in thePDCP sublayer is not essential and may be omitted.

The BB-PHY unit 124 is selectively coupled to the layer-2 unit 113A or113B. Specifically, the BB-PHY unit 124 receives, from the layer-2 unit113A or 113B, a data stream (e.g., MAC PDUs, a transport channel)obtained after the layer-2 processing, and generates modulation symboldata (or OFDM symbol data). Further, the BB-PHY unit 124 receives thebaseband reception signal stream from the RF-PHY unit 13, generates anuplink data stream (e.g., MAC PDUs, a transport channel), and suppliesthis to the layer-2 unit 113A or 113B.

The radio base station 8 according to this embodiment is configured toselect one of the layer-2 units 113A and 113B to be used. Accordingly,the radio base station 8 can select which one of the REC 8A and the RE8B is used to perform the layer-2 signal processing, depending on theneed to be preferentially met among the plurality of needs, such as theneed for reducing the processing load of the REC 8A, and the need forachieving the cooperative control among the plurality of REs 8B.

When the layer-2 unit 113A of the REC 8A is used, the radio base station8 can relatively easily perform the cooperative transmission andreception (e.g., CoMP). This is because the scheduler 20 only needs tocontrol the layer-2 unit 113A, which is arranged in the REC 8A, uponexecution of dynamic scheduling. Further, even when the layer-2 unit113A of the REC 8A is used, the data stream that contains the user dataand is transmitted through the transmission line 40 does not includeredundant data generated as a result of channel coding (e.g., blockcoding, convolutional coding, or turbo coding). This is because theBB-PHY unit 124 that performs channel coding/decoding is arranged in theRE 8B. Accordingly, the radio base station 8 can suppress the dataamount to be transmitted between the REC 8A and the RE 8B, regardless ofwhich one of the layer-2 units 113A and 113B is used.

FIGS. 15A and 15B show the details of the functional layout in the radiobase station 8 regarding the downlink transmission of user data in theE-UTRA. The functional layout shown in FIG. 15A corresponds to the casewhere the layer-2 unit 113A of the REC 8A is used in the configurationexample of FIG. 14. On the other hand, the functional layout shown inFIG. 15B corresponds to the case where the layer-2 unit 113B of the RE8B is used. In the example of FIG. 15A, MAC-PDUs (i.e., a transportchannel) are transferred from the REC 8A to the RE 8B. In the example ofFIG. 15B, the user data before performing the layer-2 processing istransferred from the REC 8A to the RE 8B.

Other Embodiments

The radio base stations 1 to 8 respectively described in the first toeighth embodiments may be relay stations. The relay station establishesa first radio link (a backhaul link) with a base station and establishesa second radio link (an access link) with a mobile station, therebyrelaying data between the base station and the mobile station.

The bearer termination units, the layer-2 units, the BB-PHY units, andthe schedulers, which are described in the first to eighth embodiments,may be implemented by using a semiconductor processing device including,for example, an ASIC (Application Specific Integrated Circuit) and a DSP(Digital Signal Processor). These units may be implemented by causing acomputer, such as a microprocessor, to execute a program.

This program can be stored and provided to a computer using any type ofnon-transitory computer readable media. Non-transitory computer readablemedia include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as floppy disks, magnetic tapes, hard disk drives, etc.), opticalmagnetic storage media (e.g., magneto-optical disks), CD-ROM (Read OnlyMemory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM,PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (RandomAccess Memory), etc.). The program may be provided to a computer usingany type of transitory computer readable media. Examples of transitorycomputer readable media include electric signals, optical signals, andelectromagnetic waves. Transitory computer readable media can providethe program to a computer via a wired communication line, such aselectric wires and optical fibers, or a radio communication line.

The first to eighth embodiments can be combined as appropriate.Furthermore, the present invention is not limited to the embodimentsdescribed above, and can be modified in various manners withoutdeparting from the gist of the invention described above.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2011-257477, filed on Nov. 25, 2011, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   1-8 RADIO BASE STATIONS-   1A-7A RADIO EQUIPMENT CONTROLLERS (REC)-   1B-7B RADIO EQUIPMENT (RE)-   10, 10A, 10B BEARER TERMINATION UNITS-   11A, 11B BB UNITS-   13 RF-PHY UNIT-   14 ANTENNA-   20 SCHEDULER-   20A PRIMARY SCHEDULER-   20B SECONDARY SCHEDULER-   20C FIRST SCHEDULER-   20D SECOND SCHEDULER-   21, 21A, 21B BUFFERS-   30, 31 INTERNAL INTERFACES-   40 TRANSMISSION LINE-   50 CONTROLLER-   51 HANDOVER CONTROL UNIT-   110 PDCP UNIT-   111 RLC UNIT-   112 MAC UNIT-   113A, 113B LAYER-2 UNITS-   120 CODING UNIT-   121 MODULATION UNIT-   122 RESOURCE MAPPING UNIT-   123 IFFT UNIT-   124, 124A, 124B BB-PHY UNITS-   130 UP-CONVERTER-   131 AMPLIFIER

The invention claimed is:
 1. A radio station that is used in a radiocommunication network and is capable of transmitting and receiving userdata including downlink user data and uplink user data to and from aplurality of mobile stations via an air interface, the radio stationcomprising: a first part; and at least one second part that can bearranged so as to be physically separated from the first part and isconnected to the first part via a transmission line so as to be able tocommunicate with the first part, wherein the first part comprises: afirst scheduling unit configured to perform dynamic scheduling toallocate a plurality of radio resources to the plurality of mobilestations or the user data; and a first signal processing unit capable ofperforming digital signal processing in order to transmit the downlinkuser data to the air interface and to restore the uplink user data froma signal received from the air interface, the second part comprises: asecond signal processing unit capable of performing, instead of thefirst signal processing unit, digital signal processing for a firstmobile station connected to the second part; and an analog signalprocessing unit configured to perform analog signal processing includingat least one of frequency conversion and power amplification to providean air interface to the first mobile station, the radio station isconfigured to alternatively use one of the first and second signalprocessing units for the digital signal processing for the first mobilestation, and one of the first and second signal processing units to beused is selected based on a security level of the user data.
 2. Theradio station according to claim 1, wherein the digital signalprocessing performed by each of the first and second signal processingunits includes at least a part of layer-2 and physical layer basebandsignal processing in order to transmit the downlink user data to the airinterface and to restore the uplink user data from a signal receivedfrom the air interface.
 3. The radio station according to claim 1,wherein one of the first and second signal processing units to be usedis selected based on an amount of traffic to be processed by the radiostation, the first part, or the second part.
 4. The radio stationaccording to claim 3, wherein when the amount of traffic to be processedby the second part is less than a predetermined level, the second signalprocessing unit is selected for the digital signal processing.
 5. Theradio station according to claim 1, wherein the first part isconnectable to a plurality of second parts, and one of the first andsecond signal processing units to be used is selected based on anecessity to perform a cooperative control among the plurality of secondparts.
 6. The radio station according to claim 1, wherein one of thefirst and second signal processing units to be used is selected based onpower consumption of the radio station.
 7. The radio station accordingto claim 1, wherein one of the first and second signal processing unitsto be used is selected based on a load status of at least one of thefirst and second parts.
 8. The radio station according to claim 7,wherein when a load of the first part exceeds a predetermined level, thesecond signal processing unit is selected for the digital signalprocessing.
 9. The radio station according to claim 1, wherein one ofthe first and second signal processing units to be used is selectedbased on processing capacity of the first or second signal processingunit.
 10. The radio station according to claim 9, wherein when theprocessing capacity of the second signal processing unit is less than apredetermined level, the first signal processing unit is selected forthe digital signal processing.
 11. The radio station according to claim1, wherein one of the first and second signal processing units to beused is selected based on a power supply status with respect to thefirst part.
 12. The radio station according to claim 11, wherein thepower supply status includes a charging status of a battery thatsupplies power to the first part.
 13. The radio station according toclaim 1, wherein one of the first and second signal processing units tobe used is selected based on a power supply status with respect to thesecond part.
 14. The radio station according to claim 13, wherein thepower supply status includes availability of self-generation of a powersupply unit configured to supply power to the second part.
 15. The radiostation according to claim 1, wherein one of the first and second signalprocessing units to be used is selected based on a QoS class of the userdata.
 16. The radio station according to claim 1, wherein one of thefirst and second signal processing units to be used is individuallyselected for each of the user data.
 17. The radio station according toclaim 1, wherein one of the first and second signal processing units tobe used is individually selected for each bearer encrypted between anupper network and the radio station.
 18. The radio station according toclaim 1, wherein the radio station determines which one of the first andsecond signal processing units is used, further based on an instructionfrom an external device.
 19. The radio station according to claim 1,wherein the first and second parts each further comprise a bearertermination unit configured to terminate a plurality of bearersencrypted between an upper network and the radio station, and the radiostation is configured to select termination points of the plurality ofbearers between the first and second parts.
 20. The radio stationaccording to claim 19, wherein one of two bearer termination units ofthe first and second parts to be used is determined in accordance with aselection of one of the first and second signal processing units to beused.
 21. The radio station according to claim 1, wherein when thesecond signal processing unit is selected for channel coding and channeldecoding, the second part sends, to the first part, informationnecessary for the dynamic scheduling.
 22. The radio station according toclaim 1, wherein the first part further comprises: a bearer terminationunit configured to terminate a plurality of bearers encrypted between anupper network and the radio station; and a buffering unit configured tostore the downlink user data obtained by terminating the plurality ofbearers, and the first part is configured to transfer, upon handover ofthe first mobile station, downlink user data pertaining to the firstmobile station stored in the buffering unit to a base station as ahandover target.
 23. The radio station according to claim 1, wherein thedigital signal processing performed by each of the first and secondsignal processing units includes at least one of: (i) addition of alayer-2 header; (ii) data segmentation/concatenation; (iii) compositionof a transfer format by data multiplexing; (iv) channel coding; and (v)modulation, so as to transmit the downlink user data to the airinterface, and the digital signal processing performed by each of thefirst and second signal processing units includes at least one of: (i)demodulation; (ii) channel decoding; (iii) decomposition of a transferformat; (iv) de-segmentation/de-concatenation; and (v) removal of alayer-2 header, so as to restore the uplink user data from a signalreceived from the air interface.
 24. The radio station according toclaim 1, wherein the second part further comprises a second schedulingunit configured to operate in a cooperative manner with the firstscheduling unit for the dynamic scheduling.
 25. The radio stationaccording to claim 24, wherein the second scheduling unit calculates aparameter used for the dynamic scheduling based on a radio communicationquality, and sends the parameter to the first scheduling unit.
 26. Theradio station according to claim 24, wherein the second scheduling unitexecutes scheduling for re-transmission of the downlink user data. 27.The radio station according to claim 1, wherein the second part furthercomprises a second scheduling unit configured to perform, instead of thefirst scheduling unit, at least a part of dynamic scheduling for userdata to be processed by the second signal processing unit, the secondscheduling unit being selectively used in accordance with the use of thesecond signal processing unit.
 28. The radio station according to claim1, wherein the radio station is a base station or a relay station.
 29. Amethod of processing user data performed by a radio station, the radiostation being used in a radio communication network and configured totransmit and receive user data including downlink user data and uplinkuser data to and from a plurality of mobile stations via an airinterface, the radio station including a first part and at least onesecond part that can be arranged so as to be physically separated fromthe first part and is connected to the first part via a transmissionline so as to be able to communicate with the first part, the first partincluding a first signal processing unit capable of performing digitalsignal processing in order to transmit the downlink user data to the airinterface and to restore the uplink user data from a signal receivedfrom the air interface, the second part including a second signalprocessing unit capable of performing, instead of the first signalprocessing unit, digital signal processing for a first mobile stationconnected to the second part, the processing method comprisingalternatively using one of the first and second signal processing unitsfor the digital signal processing for the first mobile station, whereinthe alternatively using comprises selecting one of the first and secondsignal processing units to be used based on a security level of the userdata.
 30. The method according to claim 29, wherein the digital signalprocessing performed by each of the first and second signal processingunits includes at least a part of layer-2 and physical layer basebandsignal processing in order to transmit the downlink user data to the airinterface and to restore the uplink user data from a signal receivedfrom the air interface.
 31. The method according to claim 29, whereinthe alternative using includes selecting one of the first and secondsignal processing units to be used, based on an amount of traffic to beprocessed by the radio station, the first part, or the second part. 32.The method according to claim 31, wherein the selecting includesselecting the second signal processing for the digital signal processingwhen the amount of traffic to be processed by the second part is lessthan a predetermined level.
 33. The method according to claim 29,wherein the first part is connectable to a plurality of second parts,and the alternative using includes selecting one of the first and secondsignal processing units to be used, based on a necessity to perform acooperative control among the plurality of second parts.
 34. The methodaccording to claim 29, wherein the alternative using includes selectingone of the first and second processing units to be used, based on powerconsumption of the radio station.
 35. The method according to claim 29,wherein the alternative using includes selecting one of the first andsecond signal processing units to be used, based on a load status of atleast one of the first and second parts.
 36. The method according toclaim 35, wherein the selecting includes selecting the second signalprocessing unit for the digital signal processing when a load of thefirst part exceeds a predetermined level.
 37. The method according toclaim 29, wherein the alternative using includes selecting one of thefirst and second signal processing units to be used, based on processingcapacity of the first or second signal processing unit.
 38. The methodaccording to claim 37, wherein the selecting includes selecting thefirst signal processing unit when the processing capacity of the secondsignal processing unit is less than a predetermined level.
 39. Themethod according to claim 29, wherein the alternative using includesselecting one of the first and second signal processing units to beused, based on a power supply status with respect to the first part. 40.The method according to claim 39, wherein the power supply statusincludes a charging status of a battery that supplies power to the firstpart.
 41. The method according to claim 29, wherein the alternativeusing includes selecting one of the first and second signal processingunits to be used, based on a power supply status with respect to thesecond part.
 42. The method according to claim 41, wherein the powersupply status includes availability of self-generation of a power supplyconfigured to supply power to the second part.
 43. The method accordingto claim 29, wherein the alternative using includes selecting one of thefirst and second signal processing units to be used, based on a QoSclass of the user data.
 44. The method according to claim 29, whereinone of the first and second signal processing units to be used isselected for each of the user data.
 45. The method according to claim29, wherein one of the first and second signal processing units to beused is selected for each bearer encrypted between an upper network andthe radio station.
 46. The method according to claim 29, wherein thefirst and second parts each further include a bearer termination unitconfigured to terminate a plurality of bearers encrypted between anupper network and the radio station, and the method further comprisesselecting termination points of the plurality of bearers between thefirst part and the second part.
 47. The method according to claim 46,wherein one of two bearer termination units of the first and secondparts to be used is determined in accordance with a selection of one ofthe first and second signal processing units to be used.
 48. The methodaccording to claim 29, further comprising sending, from the second partto the first part, information necessary for the dynamic scheduling,when the second signal processing unit is selected for channel codingand channel decoding.
 49. The method according to claim 29, furthercomprising: terminating, at the first part, a plurality of bearersencrypted between an upper network and the radio station; buffering, atthe first part, the downlink user data obtained by terminating theplurality of bearers; and transferring, upon handover of the firstmobile station, the buffered downlink user data pertaining to the firstmobile station to a base station as a handover target.
 50. The methodaccording to claim 29, further comprising performing, at the secondpart, secondary scheduling for the dynamic scheduling in a cooperativemanner with the first part.
 51. The method according to claim 50,wherein the secondary scheduling includes calculating a parameter usedfor the dynamic scheduling based on a radio communication quality, andsending the parameter to the first part.
 52. The method according toclaim 50, wherein the secondary scheduling includes executing schedulingfor re-transmission of the downlink user data.
 53. The method accordingto claim 29, wherein the second part further includes a secondscheduling unit configured to perform, instead of the first schedulingunit, at least a part of dynamic scheduling for user data processed bythe second signal processing unit, and the method further comprisingselectively using the second scheduling unit in accordance with the useof the second signal processing unit.